The present invention relates generally to tailoring of composite material structures, and more particularly to the tailoring for yield-type response in composite material members subject to tensile loading, with direct applicability to the arresting of moving bodies and the maximization of kinetic energy dissipation by an arresting member within a set of displacement and deceleration force constraints.
The problem of arresting a moving body with constraints imposed upon the values of maximum deceleration and maximum distance (or displacement) over which to perform the arrest is frequently encountered, particularly in the fields of aerospace and automotive engineering. Typical constraints stem from payload/passenger deceleration tolerance limits and/or distance available for the arrest.
Several solutions for this problem have been proposed, and some of them are well established. Fundamentally, existing solutions can be divided into two classes: arresting mechanisms and structural arresting devices.
The first class is represented by aircraft carrier cable arrest systems and inertial/centrifugal braking devices used in association with cables, mechanisms generally characterized by good reliability and performance. However, their complexity and their weight represent drawbacks and a limitation for their use.
The second class is represented by crushable subfloors, which are commonly used in aerospace designs, crumpling zones, which are commonly used in vehicle designs, or a bungee cord, which is used today primarily for recreation. While of comparatively reduced weight and complexity, the systems in this class are also capable of performing the function of decelerating/arresting a payload.
Composite materials are playing an increasing role in structural applications. These materials combine high specific strength and stiffness with a high degree of anisotropy, which makes them attractive candidates for use in many designs. A large volume of research addressing the subject of composite materials has established their usefulness for structural applications.
One important problem that occurs when structural solutions are employed for constrained arrest of a moving body stems from the rapid increase in arresting force that is developed as a function of the structural deformation. Consider, for example, the operation of a bungee cord. The arresting force starts from zero when the chord is just taut and continuously increases with the amount of stretching applied thereby subjecting the payload to a proportionately increasing deceleration. Consequently, the constraint on the maximum level of deceleration admissible may be violated. This effect is even more significant in the case of structures characterized by a higher stiffness, such as a fuselage or a subfloor. Solutions incorporating crushable subfloors attempt to alleviate this problem by designing a structure with a flatter arresting force versus displacement response. However, because a subfloor has an arresting displacement capability that is limited to a value generally on the order of the floor thickness, this flat response translates into limited energy dissipation. On the other hand, a structure that is too compliant will either exceed the displacement constraint or exceed the maximum strain level accepted by the material of the structure and fail without having dissipated the necessary amount of energy.
Accordingly, what is sought is a structural member for arresting a payload that maximizes the amount of energy dissipated within a set of constraint values for both maximum deceleration force and distance over which the arrest is performed.